1. Field of the Invention
This invention relates to a nucleic acid-containing complex characterized by containing a nucleic acid, and a positively-charged water-insoluble biodegradable polymer, and also relates to a method for controlling the rate of release of the nucleic acid from the complex.
The invention is also concerned with phagocytic cells (hereinafter referred to as phagocytes) comprising a nucleic acid-containing complex containing a nucleic acid and a biodegradable polymer. The invention also concerns a drug having the nucleic acid-containing complex as an active ingredient and usable for phagocyte-mediated gene therapy.
2. Description of the Related Art
In recent years, as molecular genetic factors of human diseases have become clear, more and more emphasis has been placed on studies of gene therapy. Gene therapy is aimed at expressing DNA at a targeted site or cell. For this therapy, it would be beneficial to bring the DNA directly to the target site or cell, transfer it into the target site or cell efficiently, and express it at the specific site or in the cell functionally. Various methods have been reported for the effective transfer and expression of foreign DNA (Fumimaro Takaku, eds. “Idenshichiryo no Saizensen: Kisogijutu kara Rinsho Oyo made (The Forefront of Gene Therapy, from Basic Technology to Clinical Applications)”, Experimental Medicine, Vol. 12, No. 15, 1994; Robert E. Sobol and Kevin J. Scanlon, The Internet Book of Gene Therapy, Appleton & Lange Stamford, Conn., 1995). They are roughly classified into (1) physical methods for DNA transfer (microinjection, electroporation), (2) chemical methods for DNA transfer (calcium phosphate transfection, DEAE-dextran transfection), and (3) biological methods (virus vectors, such as retroviruses and adenoviruses). The existing chemical methods, such as calcium phosphate transfection, and DEAE-dextran transfection, are generally low in the efficiency of gene transfer. The physical methods, such as microinjection and electroporation, may require special devices, and they are not practical for routine clinical use. Virus vectors have been expected to find clinical applications because of their high efficiency of gene transfer. However, these vectors involve the risk of adverse reactions such as immune reactions, due to their nature as viruses.
To overcome the above drawbacks, new technologies have been developed. Liposome methods incorporate gene into liposomes to protect the gene from inactivation or degradation. The liposomes are free from viral DNA, and thereby rule out the possibility that potentially dangerous recombination events may occur. However, their potent toxicity to a variety of cell types restricts the use of liposomes as carriers of DNA. Development of new substances and means for gene delivery continues even now.
In the field of gene therapy for vascular lesions, the so-called hydrogel method has also been developed which comprises adhering a hydrogel to the surface of a catheter to be introduced into a blood vessel, placing a plasmid gene in the hydrogel, and directly coating the hydrogel into the blood vessel (Marchall, E., Science, 269, 1050–1055, 1995). According to this method, the plasmid is slowly released from the hydrogel by simple diffusion. With this method, in general, both the period of slow release is brief, and this period is difficult to control both with respect to rate and length. Gene therapy requires that the amount of the therapeutic gene or the period of its supply be adjusted depending on the disease to be treated or the status of the disease. Thus, there is a demand for a method capable of controlling the period of slow release of the therapeutic gene according to the requirements of therapy.
When a foreign gene is to be used in a clinical setting such as gene therapy, a persistent supply of this gene at a stable level to the target site is necessary for the functional expression of the gene.
Furthermore, studies of gene therapies using antisense oligonucleic acids have attracted attention in recent years. Means for supplying such nucleic acids site-specifically and stably in vivo for controlled periods of time should enhance the efficacy of such an approach.